1. Field of the Invention
This invention relates to methods and apparatus for flanging tubular polymer articles, and more specifically to the flanging of the open ends of tubular articles of thermoplastic polymers, particularly of saturated linear polyester materials such as polyethylene terephthalate. The tubular articles may be open at both ends or may have one open end and one closed end (integral or otherwise). The tubular articles may be of circular, rectangular or other cross-section.
2. Description of Related Art
Our published British Patent Application No. 8319768 (publication No. 2143461A) discloses and claims a method of flanging a tubular article of a crystallisable thermoplastic polymer which has been drawn and heat-set to an elevated temperature, leaving the material with a residual shrinkage capability, comprising the steps of: applying an end of the tubular article to a flanging die which engages the inner surface of the end, heating the said end of the tubular article to a flanging temperature, at which the said crystallisable thermoplastic polymer is softened, the flanging temperature being above the glass transition temperature of the polymer but below the elevated temperature to which it has been heat-set, forcing the tubular article and the die together, so that the heat-softened end of the tubular article is forced by the die to move outwards to form a flange, the material of which undergoes residual shrinkage to establish well-defined flange dimensions as the polymer takes up the contours of the die, and then causing the flanged end of the tubular article to cool whilst restrained against deformation to set the flange in accordance with said well-defined dimensions.
That patent application also discloses and claims apparatus for flanging tubular articles of a crystallisable thermoplastic polymer which has been drawn and heat-set to an elevated temperature, comprising: a pair of flanging dies, arranged to engage opposite ends of one of the tubular articles for forming an outward flange simultaneously at both ends of the tubular article, means for forcing the dies towards each other, and means for heating and means for cooling the said ends of the tubular article.
In the specific examples described in Application No. 8319768, the heating and cooling of the flanged end are both effected while it is in contact with the flanging die. This requires the flanging die to be heated to the flanging temperature and then to be cooled to a temperature which in practice is at least 20.degree. C. (typically 40.degree. C.) below the flanging temperature to set the flange. Such thermal cycling is inefficient, wasteful of energy and time consuming.